In the following discussion certain articles and methods will be described for background and introductory purposes. Nothing contained herein is to be construed as an “admission” of prior art. Applicant expressly reserves the right to demonstrate, where appropriate, that the articles and methods referenced herein do not constitute prior art under the applicable statutory provisions.
Optical density (OD), measured in a spectrophotometer, can be used as a measure of the concentration of cells in suspension. As visible light passes through a cell suspension, the light is scattered. Greater scatter indicates that more cells are present. Typically when working with a particular type of cell, one determines optical density at a particular wavelength that correlates with the growth media used. For bacteria, generally cells are grown in, e.g., LB broth, and OD600 is measured.
To determine the OD of a cell culture, typically a quartz cuvette is used with a benchtop spectrophotometer. A wavelength is selected on the spectrophotometer, and a cuvette containing a control liquid (e.g., a blank)—almost always the growth medium in which the cells are being incubated—is inserted into the sample compartment within the spectrophotometer. A transmittance/absorbance control is then set to 100% transmittance. Once the control is adjusted for 100% transmittance, turbidity measurements can be made. The blank is removed, and then an aliquot of the sample to be measured is pipetted into another cuvette and the cuvette is inserted into the sample compartment. The spectrophotometer will then indicate the OD and percent transmittance of the sample. One drawback to using this traditional method for measuring OD is that it requires human intervention; that is, aliquots of the sample to be measured must be taken at intervals, loaded into cuvettes, and inserted into the spectrophotometer to get a reading. Not only does this procedure require time and effort, but invasively accessing the growing cell culture runs a risk that the cell culture may be contaminated. Further, the cell culture is depleted with each sample removed. An additional drawback is that once the cells are growing, it is difficult to predict when the cells will reach a target OD.
Accordingly, there is a need in the art for a cell growth device that noninvasively, rapidly, predictably and reproducibly promotes growth in a variety of cell types while automatically measuring the OD of the cells in the vessel in which they are growing. Additionally, there is a need in the art for a cell growth device that controls the growth of the cells to a target OD at a target time as requested by a user. Such a cell growth device can function either as a stand-alone device, e.g., benchtop device, or the cell growth device can be employed as one module in a multi-module automated cell processing system. The disclosed cell growth devices and methods address these needs.